This invention relates to improved circuitry for producing computer controlling signals in response to the actuation of the different keys of a keyboard, as for instance in small electronic desk calculators and the like.
In certain types of computer keyboard arrangements, it is conventional to utilize an X-Y array of key controlled switches, each adapted to feed into the computer or calculator a signal representing a particular number or other element of data, or to deliver a predetermined command for commencing a desired arithmetical operation or the like. Two sets of intersecting input and output lines are connected to the switches, with each line having associated with it a series of such switches, and with each switch serving to connect one of the input lines to a predetermined one of the output lines. A series of timed pulses are supplied to each of the input lines, for ultimate delivery through the various output lines to the other circuitry of the computer when different ones of the switches are closed. An additional circuit, preferably including a flip flop and shift register, acts upon closure of any of the switches to produce a "Start" signal, which is utilized in reading and interpreting the output pulses.
One major difficulty which has been encountered with this type of keyboard circuitry has resided in its susceptibility to formation of spurious start signals as a result of chattering or bouncing of the switch contacts during actuation. It is extremely difficult for an operator to always press and release all keys with a sufficiently uniform, positive and rapid motion to assure only a single uninterrupted closure of the switch upon each actuation. If a switch in a conventional keyboard circuit first closes, then opens for a short interval, and then closes again, all during a single actuation of the switch, the circuit may produce two separate start signals, resulting in the delivery of incorrect data or an incorrect command to the remainder of the computer.